This invention relates generally to air ducts used in commercial and residential HVAC systems. Additionally, this invention pertains to HVAC air duct systems and methods for fabrication and assembly of air duct systems.
The fabrication and installation of ductwork for use in residential and commercial HVAC systems is an expensive and time-consuming process. Duct work in prior art HVAC system typically includes rigid metal duct and fittings, as shown in FIG. 1. These ducts are heavy and usually need an extensive external support system. They have very poor insulation qualities and are difficult to cut, trim and fit on-site. In some applications, flexible insulated duct is used but these flexible ducts have little integral structural support and are susceptible to being crushed or damaged during normal installation handling. Improper fittings contribute to the inefficiency of prior art systems. The poor insulation qualities of the prior art duct systems require the system to extend its run time to replace the conditioned air lost due to inefficiencies. This contributes to an overall less efficient system.
The following patents and publications help illustrate the state of the art and are all expressly incorporated by reference in their entirety.
U.S. Pat. No. 5,210,947 to Donnelly discloses a process of manufacturing a duct by extruding a tubular casing composed of a polymeric foam.
U.S. Pat. No. 4,615,411 to Breitscheidel, et al. discloses a flow duct for conveying air that has an outer layer of molded thermoplastic closed cell foam material.
U.S. Pat. No. 5,487,412 to Matthews, et al. discloses a glass fiber air duct for conveying an air stream. It is coated with a polymeric coating comprising an organic biocide.
U.S. Pat. No. 5,795,634 to Fukui discloses a noise reducing duct that comprises an open-cell foam layer formed by helically winding and open cell foam resin banded onto an outer circumferential face of a inner layer.
U.S. Pat. No. 5,944,060 to MacKay discloses a composite duct system that comprises a fiber reinforced resin system and a foam portion that is formed of fire retarding material derived from a resin system.
U.S. Pat. No. 6,062,270 to Hultberg, et al. discloses a double-walled ventilation duct system with an inner tube, an outer tube, and arranged therebetween, a sound-absorbing material. The sound absorbing material may be wool, or other sound-absorbing material.
U.S. Pat. No. 5,634,847 to Shea discloses a fiberglass reinforced plastic fume exhaust system that includes duct walls therein covered with multiple thermoplastic resins which melt when exposed to high temperatures.
G. F. Baumann, et al., Alternate Blowing Agent Options And Polyisocyanurate Laminate Foams, 32nd Annual Polyurethane Technical/Marketing Conference, 1989, summarize the CFC alternate options for Class I PIR laminate foams.
Ohnuma, et al., Urethane Modified Polyisocyanurate Foams For Spray Application, 32nd Annual Polyurethane Technical/Marketing Conference, 1989, disclose a foam spray system with improved flame retardancy.
Gluck, et al., Carbon Black-Filled Foam Insulations, 32nd Annual Polyurethane Technical/Marketing Conference, 1989, disclose the advantages of the addition of carbon black-filler to isocyanurate foams.
U.S. Pat. No. 3,899,005 discloses a modular duct system for flexible, elongated articles such as telephone cables. The duct system of this invention comprises conduits formed of translucent, resin bonded glass fibers.
U.S. Pat. No. 3,819,209 discloses a duct connector that included a collar made of flexible material having a flange at one end thereof extending around its periphery.
What is needed, then, is a duct system for HVAC systems that is rigid, insulated, relatively light in weight, and is easy to install and connect on site in a variety of configurations.
The present invention provides a duct, duct system, and an HVAC system comprising the ducts of the present invention that achieve the goals of providing well insulated, light weight ducts that are cost effective and easy to handle and install.
The present invention overcomes the limitations of the prior art by using multiple sections of rigid foam duct in the assembly of a residential or commercial HVAC air duct system. Although many different duct work shapes are feasible, each piece of duct is preferably formed into a square, rectangular or round pipe configuration (of various lengths and sizes) from a cellular polymeric material. The round pipe configuration is most preferable. Furthermore, the polymeric material is preferably a polyurethane material.
The duct sections may include end and/or side branch fittings that allow for easy interconnection of different duct sections in order to form a complete system. Thus, the duct sections can be used to quickly assemble and install HVAC duct systems of varying configurations on-site. The polyurethane material provides rigidity and insulative qualities while being light in weight and easy to handle.
One embodiment of the present invention is an air duct that comprises one or more air duct segments. Each segment is disposed longitudinally relatively to an axis parallel to air flow, and each segment comprises a wall that defines an internal space that permits flow of air. The wall has an outer shell, an inner shell, and a first core layer disposed between the outer shell and the inner shell. The core comprises a polymeric cellular material, or foam.
Another embodiment of the present invention is an air duct system that comprises a primary air duct, at least one secondary air duct, and at least one branch duct. Each of the aforementioned ducts comprises a wall that has an outer shell, an inner shell, and a core layer positioned between the outer and inner shells. The core layer of each duct comprises a cellular thermoset polymeric material.
Finally, another embodiment of the present invention is an HVAC system that comprises an HVAC unit for thermally conditioning air, a blower to direct the thermally conditioned air, a primary air duct to receive the conditioned air, and to discharge the conditioned air to conditioned space, at least one branch line duct to further direct conditioned air to conditioned space; and a control unit to control the blower. In this embodiment, the primary air duct and the at least one branch line duct comprise a thermoset resin material, have an R value of at least 5, and a density of from about 1.5 pounds per cubic foot to about 4 pounds per cubic foot.